Electronic vacuum advance for an ignition system

ABSTRACT

A vacuum servodevice connected to an internal combustion engine is operated in accordance with engine load to vary the position of a core electrically coupling first and second windings of a transformer. By changing the coupling between the windings the output of the transformer is changed. This variable output from the transformer is used to control the conduction of a transistor amplifier which provides a modulating bias on a potential representing ignition advance relative to engine r.p.m. which is connected to the gate of a high sensitivity silicon-controlled rectifier (SCR) which acts as a voltage level detector. The SCR is triggered when the modulated potential reaches a given level providing a firing pulse to discharge the ignition capacitor. The time required for the modulated potential to reach this triggering level varies according to engine r.p.m. and vacuum.

i United States Patent [72] Inventors Arthur Hulton Elk Grove; Peter Dogadko, Chicago, Ill. [21] Appl. No. 777,719 [22] Filed Nov. 21, 1968 [45] Patented Jan. 12, 1971 [73] Assignee Motorola, Inc.

' Franklin Park, Ill.

a corporation of Illinois [54] ELECTRONIC VACUUM ADVANCE FOR AN IGNITION SYSTEM 7 Claims, 7 Drawing Figs. I [52] US. Cl 123/148, 315/209 [51 Int. Cl vF02p 3/02 [50] Field of Search 123/ 1485; 315/209, 209CD, 214

[56] References Cited UNITED STATES PATENTS 3,277,875 10/1966 Miki 123/148E 3,356,896 12/1967 Shano ABSTRACT: A vacuum servo device connected to an internal combustion engine is operated in accordance with engine load to vary the position of a core electrically coupling first and second windings of a transformer. By changing the coupling between the windings the output of the transformer is changed. This variable output from the transformer is used to control the conduction of a transistor amplifier which provides a modulating bias on a potential representing ignition advance relative to engine r.p.m. which is connected to the gate of a high sensitivity silicon-controlled rectifier (SCR) which acts as a voltage level detector. The SCR is triggered when the modulated potential reaches a given level providing a firing pulse to discharge the ignition capacitor. The time required for the modulated potential to reach this triggering level varies according to engine r.p.m. and vacuum.

" TRANSDUCER I27 "7 PATENTEDJAN 1m 3554-177 SHEET 1 UF 2 TRANSDUCER IZO/ lNVENTORS ARTHUR s. HUFTON BY PETER' DOGADKO ATTYS.

BACKGROUND OF Tins INVENTION This invention relates to ignition systems for internal combustion engines, and more particularly to an improved ignition system which electronically provides ignition timing relative to both engine r.p.m. and vacuum.

In more advanced systems introduced in the past, ignition timing has been accomplished electronically for advancing the spark relative to increased engine r.p.m. For the most part, it has not been possible in these systems to meet manufacturer's specifications with respect to timingbecause such systems have not taken into consideration the changes required in timing due to sudden changes in engine loadln conventional breaker point systems this advance is provided by a mechanical, vacuum advance servomechanism. I I

SUMMARY OF THE INVENTION It is an object of this invention 'to provide a new and improved electronic ignition system. 7 1

It is another object of this invention to provide an ignition system which is capable of meeting the manufacturers required ignition timing for most internal combustion engines.

It is a further object of this invention to provide an electronic ignition system which provides ignition timing dependent on both engine r.p.m. and engine vacuum or load.

In one specific embodiment of this IIIVIIIIOI1,'3 pulse generator is driven in synchronism with an internal combustion engine for producing electrical pulses. A semiconductor-triggering device is responsive to the pulses reaching a given level to discharge the capacitor of the ignition system to produce an ignition pulse for the engine. The generated pulses reach the given level in a timed relation to'the engine r.p.m. to provide ignition timing. The ignition capacitor subsequent to being discharged is charged through the action of a blocking oscillator. A variable reluctancetransformer having primary and secondary windings is'connected to the blocking oscillator and has a movable core positioned therein for varying the magnetic coupling between the windings. -A transistor amplifier circuit is connected between the transformer and the control electrode of the semiconductor trigger, the output of which modulates the pulses from the generator; The core of the transformer is connected to a vacuum servo and changes position within the transformer in response to' engine load to vary the coupling between the primary and secondary windings thereof to vary the output of the transformer. The output of the transformer is connected to the base of the transistor amplifier and controls the output therefrom. Therefore, as the engine load or vacuum varies, the core changes position within the transformer to vary the output. This changes the output voltage of the transistor amplifier to modulate the level of the potential on the control electrode of the, semiconductor trigger. As the potential level is varied on the control electrode, the time required for the generated voltage to reach the given level to discharge the capacitor varies, hence the ignition timing changes with both engine r.p.m. and load.

DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION The ignition circuit illustrated in FIG. 1 is to be used with an eight-cylinder engine having a four-stroke cycle. Thus four cylinders will go through their power stroke for each revolution of the flywheel. It should be understood that the invention is not limited to an eight-cyclinder engine but would also be operative in engines having a greater or smaller number of cylinders. Each of the cylinders of the internal combustion engine I0 is provided with a spark gap or spark plug "-18 and separate ignition coils 20-27. The secondary windings of each of the coils 20-27 are connected across the respective spark gaps 11-18.

Operation of the ignition system will be described utilizing only the ignition coil 20 and spark gap 11; it being understood that the remaining ignition coils and spark gaps function in a similar manner. I

A' semiconductor trigger or siliconcontrolled rectifier (SCR) 30 connects the parallel connected ignition coils 20 and 22 in series with an ignition capacitor 32. Of the two cylinders associated with ignition coils 20 and 22, one is ready to be fired and the other is on exhaust stroke. Thus, only the cylinder to be fired is effected by a pulse through the ignition coils 20 and 22.

A pulse generator including flywheel '38 which is driven in synchronism with the internal combustion engine 10 is used to provide triggering pulses for controlling the conduction of SCR 30. The generator also includes four variable reluctance pickup units or sensors 40-43 that are adjustably mounted in a spaced relation to the flywheel, andeach includes an inductive winding such as 45 surrounding the pole piece 46, ot pickup 40. The polepiece 46 is disposed so that it fits adjacent to the path of the shaped element 48 integral with the flywheel 38. The winding 45 is connected to a level detector comprising the SCR 50.

As flywheel 38 rotates, the element 48 passes the pole piece 46 of pickup 40 causing a change of flux in the winding 45. Flywheel 38 rotates in the direction of the arrow so that the pointed end of the shaped element 48 passes the pole piece initially. The shaped element 48 is such that the airgap between the element and the pole piece will close as the flywheel rotates past the pickup. The change in magnetic reluctance of the pickup causes the potential developed across winding 45 to rise to a given level. The time required to reach this level will vary with engine r.p.m. Since SCR 50 will not conduct to trigger SCR 130 until the potential on the gate .thereof reaches a predetermined level (about .6 of a volt), the engine capacitor is in effect discharged sooner or laterso that ignition tim ing varies at a rate depending on engine r.p.m. A more detailed description of a circuit similar to this for providing ignition timing or advance with respect to engine r.p.m. may be found in US. Pat. No. 3,356,896, issued Dec. 5, 1967 to the assignee of this application.

A blocking oscillator is used to charge the ignition capacitor 32'after it has been discharged. The blocking oscillator includes an NPN type power transistor 55 having a collector electrode 57 that is coupled by the diode 58 to the ignition switch 35. The capacitor 60 filters out any ripple in the supply voltage to the power transistor 55. The emitter 62 of transistor 55 is connected in series to primary winding 65 of transformer 66. A positive feedback path for the oscillator includes feedback winding 68 of the transformer 66, which is coupled through the parallel combination of diode 70 and resistor 71 to the base or control electrode 59 of the transistor 55. A zener diode 74 is connected between the collector and emitter of transistor 55 to limit the voltage between these two electrodes for protective purposes.

An enabling or semiconductor switching circuit 76 is provided for initiating operation of the oscillator to recharge the ignition capacitor 32 after each discharge of the capacitor by the triggering of the SCR 30 subsequent to the triggering of the SCR 50 by the pulse generator. When SCR 50 conducts it discharges the capacitor 78 through the primary winding 80 of the pulse transformer 82 which produces a potential in the secondary winding 84 to trigger the SCR 30. The enabling circuit 76 includes a transistor 85 having an emitter 86 connected to the ignition switch 35 by resistor 88. The collector 90 of the transistor 85 is connected through blocking diode 92 and resistor 94 to the control electrode of transistor 55. The base or control electrode 96 of transistor 85 is coupled by resistor 98 and blocking diode 100 to point 102, which is the junction between the discharge capacitor 32 and the SCR 50. In operation, when initially cranking the engine during starting, a pulse is generated in the winding 45 causing the capacitor 78 to discharge through transformer 82 to trigger the SCR 30 into conduction. The triggering of SCR 30 grounds the control electrode 96 of the transistor 85 through the primary winding 20 of the ignition coil. This causes transistor 85 to conduct applying a pulse to the base 59 of the transistor 55 biasing that transistor into conduction. Increasing current in the primary winding 65 of the transformer 66, induces a current in the secondary winding 68. The positive feedback network of the blocking oscillator couples the current back to the control electrode 59 to drive the transistor 55 into saturation. When the transistor 55 reaches saturation, the steady current through winding 65 no longer induces a current in winding 68. The potential is then removed from control electrode 59 and transistor 55 is rendered nonconductive. This causes the field of the transformer 66 to collapse inducing a current in winding 104 of the transformer 66, which is coupled by resistor 106 to charge the capacitor 32. Subsequently, the triggering of SCR 30a, which is connected to the next sensing unit 41 in the path of element 48, will discharge the charged capacitor 32 through the primary winding 21 to produce a firing pulse across the gap 12. The diode 110 prevents ringing in the circuit when capacitor 32 discharges.

When the field collapses a potential is developed across the primary winding 21 which charges the ignition capacitor 32 in the opposite direction. Subsequent discharge of the capacitor 32 will induce current in winding 68 of the transformer 66 to energize the oscillator. The enabling circuit 76 in addition to providing a means for charging the capacitor 32 during engine cranking also initiates operation of the oscillator at high speeds before the discharge of capacitor 32 to insure sufficient charging of the capacitor 32 prior to the next discharge cycle.

Referring to FIG. 4, line A on the graph indicates the advance curve characteristic of an engine utilizing the ignition system of FIG. 1, wherein the advance is provided by the engine driving the shaped element 48 of flywheel 38 pass the pickups 43 at a varying rate dependent on engine r.p.m. As can be seen from the curve, the advance increases proportionally with the engine r.p.m. to a maximum of approximately 32. Curve B on the graph illustrates a typical advance curve required by an engine manufacturer. It is readily apparent from this graph that the amount of advance required is greater than that available from the engine flywheel. Furthermore, in the ignition system as described so far in connection with FIG. 1, there is no way to change the spark advance with sudden changes of engine load. Confronted with this problem, we have developed a unique circuit for converting vacuum in an internal combustion engine into electrical signals which can be utilized by the ignition circuit to provide ignition timing relative to engine load, thus making it possible to have an electronic ignition system wherein spark advance may be adapted to various specifications as required by engine manufacturers.

Referring to FIG. 1, a transducer 115 is shown for convening engine vacuum into mechanical motion. The transducer is connected to a core 117 of the transformer 120, which has a primary winding 121 coupled by resistor 123 to the emitter 62 of power transistor 25 of the blocking oscillator. The secondary winding 125 of the transformer is spaced apart from the primary winding 121 and is coupled by blocking diode 127 and resistor, capacitor time base network 129 to the base 131 of the semiconductor or transistor amplifier 132. The collector 133 of transistor 132 is coupled by variable resistor 135 and a voltage divider formed by resistors 136 and 138 to the power supply through the ignition switch 35. Zener diode 140 provides a regulated power supply to the collector 133. The emitter 142 of the transistor 132 is coupled by resistors 145, I450, 145b and 145 0 through the blocking diodes 146-146c, respectively to the junctions 148-148c. For instance, the junction l38c is between the winding 45 on the pickup 40, and the gate of SCR 50. It can be seen, therefore, that conduction of transistor 132 maintains the junction points 148-l48c at a given potential and modulates the pulses generated in the winding 45 by the shaped element 48 passing the pickup 40. This modulation of the pulses causes the potential on the gate of SCR 50 to reach the given level to cause conduction of the SCR sooner than it would normally depending on the amount of bias potential at the junction point 148C.

The vacuum-controlled timing circuit operates as follows. When the blocking oscillator is energized to charge the ignition capacitor 32, a potential is coupled from the power output transistor 55 to the transformer 120. Core 117 of the transformer 120, is positioned by the transducer, which is responsive to the engine vacuum at that instant so the core at the position set by the transducer provides a degree of magnetic coupling between the primary and secondary windings whereby the output potential from the base 131 of the transistor 132 will cause that transistor to conduct an amount to provide the desired modulating or bias potential at junction point 148c.This bias potential therefore has an amplitude dependent on engine load and modulates the pulses from pickup 40 so the level of the potential on the control electrode of SCR 50 to gate it into conduction will be reached sooner than if the pulse from the pickup 40 alone has used. This causes the advance of the engine ignition timing with respect both to engine r.p.m., which determines the level of the pulses from the pickups, and engine vacuum. The thermistor 150 provides temperature stabilization for the transistor 132, and the resistor-capacitor network 129 determines the time required for a pulse from transformer 120 to trigger the transistor 132 into conduction.

Although in the preferred embodiment the transformer 120 is shown to have its input from the blocking oscillator, it could be energized by a separate oscillator, for instance, and still fall within the scope of this invention.

FIGS. 2 and 3 illustrate in detail the construction of the transducer 115 and the transformer 120. The transducer 115 includes a conventional vacuum servomechanism 152 of the type currently being used in the automotive industry to convert engine vacuum into mechanical movement for positioning the engine points to provide spark advance. A shaft 154 is connected to the diaphragm of the servo 152 (not shown). At the other end shaft 154 is connected to the ferrite core 117 which is moved within the transformer 120. As shown in FIG. 3, the transformer 120 includes a primary winding 121 and a secondary winding 122. The degree of coupling between these windings is determined by the position of the ferrite core 117 within the transformer. As the engine vacuum varies, the diaphragm causes the shaft 154 to move the core 117 within the transformer 120 thereby varying the reluctance or magnetic coupling between the transformer to vary the output potential. Various brackets 156, 158 and 160 and 162 provide means for mounting the vacuum transducer to the engine and for mounting the shaft 154 to the core 117.

Although the vacuum transducer and transformer shown in FIGS. 2 and 3 are the preferred way for generating a potential proportional to the engine vacuum, the invention is not limited to this combination alone. Additional but not all exclusive ways to produce a potential in response to a change in engine vacuum are shown in FIG. 5-7. In FIG. 5, the transducer includes a vacuum servo similar to 152, and the voltage producing means controlled by the servo 165 includes a potentiometer 167 having a wiper arm 170 that is connected to the shaft of the vacuum servo 165 and moved by the same in response to changes in engine vacuum to produce an output potential which is coupled to the level detectors.

matically at l72. ;"lhe,output;frequency oflwhich is controlled by a piezoelectric element .pcsitioned in a pressure transducer 176. A typical oscillating circuit where'the frequency is controlled 'by apiezoelectric element isshownin U.S;'Pat. 'No. 2,137,852, issued Nov, 22, l938.' Also a; type of pressure transducer which could be adapted to strain the piezoelectric element is shown in U. S. Pat. No. 3,195,353 issued July 20, l965. The output from the oscillator 172 is coupled through an integrator circuit of atype well known in the art which has a potential output dependent on the oscillator frequency. so a steady direct current bia'spotential jis coupled from the integrator circuit 178 to the level detector for providing' vacuum advance information. t

Still a further circuit for providing an output potential representing the engine vacuum is shown i'n'FlG. 7. This circuit utilizes a strain's'e'nsitive transistor or pitran 180, which has a mechanical input 182 connected to the base 184 thereof. The bias coupledto the base of the transistor by resistors 186 and 187 is modulated by varying the strain on the base through the mechanical-input" 182 coupled to. the vacuum transducer. The maximum output current is limited by resistor 190. 'I'herefore,"changes in enginefv'acuum change the strain on the base 184 of transistor 180, varying the output thereof to the level detectors to provide a potential thereto, which represents the engine vacuum. I i e What has been described, therefore, is an improved ignition system for an internal combustion engine which provides both vacuum advance and advance proportional to engine r.p'.m. electronically thereby permitting use of this ignition circuit in a wide variety of internal combustion engines which have differentignitiontimingrequirements.

Weclaim: l. A capacitor discharge ignition system foran intemal combustion engine having pulse generator means driven in synchronism with the engine for producing electrical pulses,

3. The capacitor discharge ignition system of claim I wherein said vacuum-controlled voltage generator means comprises oscillating circuit means' including' piezoelectric means forestablishing the output frequency thereof, integrating circuit means connected tothe output of said oscillating circuit means and having a voltage output dependent on the input frequency from said oscillator circuit means, and transducer means responsive to engine vacuumconnected to said piezoelectric means so the mechanical motion thereof in response tochanges in engine vacuum strains said piezoelectric means to change the frequency of the same thereby varyincluding incombination, trigger-circuit meansincluding-a semiconductor having a control electrode for operatingthe same, first circuit means coupling the pulses from the pulse generator means to the control electrode of said semiconductor, said trigger circuit means being responsive to the pulses on the control electrode of said semiconductor reaching a given level .to operate the same to discharge the ignition capacitor thereby producing an ignition pulse for the engine, the generated pulses reaching said given level in a timed relation to the engine rpm. to provide, ignition timing, second circuit means connected to the junction of said first circuit means and the control electrode of said semiconductor for establishing a direct current bias on thecontr'ol electrode, and vacuum controlled voltage generator means connected to said second circuit means, said vacuum-controlled meansfbeing responsive to the engine vacuum under changing engine loads to vary the direct current bias in said second circuit means, hence on the control electrode of said semiconductor thereby varying the time required for the pulses from the pulse generator means to reach the given level to discharge the ignition capacitor so the ignition timing depends on both engine rpm. and vacuum.

2. The capacitor wherein said vacuum-controlled voltage generator means includes a vacuum servo, a potentiometer having a wiper arm discharge ignition'system of claim 1 semiconductor.

ing the output frequency of said oscillating circuit means to vary the output potential of said integrating circuit means in accordance with engine load. 1 v 4. The capacitor discharge; ignition, system of claim 1 wherein said vacuum-contrhlled voltage generator means includes amplifier circuit means including a strain sensitive semiconductor having a mechanical input for modulating the bias thereon, transducer meansresponsive to engine vacuum, and means connecting said transducer means to said mechanical input of said semiconductor, said transducer means responding to changes in the engine load to vary the strain on said semiconductor through said mechanical input thereby changing the bias thereon to regulate the output potential of said amplifier circuit means in accordance with engine vacuum. g 5. The capacitor discharge ignition system of claim 1 wherein said second circuit means includes an electron .control device having input, output and control electrodes. with the control electrode of said semiconductor being connected to said output electrode of said electron control device, a potential source coupled tosaid input electrode, and said vacuum-controlled voltage generator means being connected to said control electrode thereof, said vacuum-controlled means being responsive to engine vacuum to produce a potential to control the conduction of said electron control device thereby varying the bias on the controlelectrode of said 6.. The capacitor discharge ignition system of claim 1 wherein said vacuum-controlled means includes oscillator means, a vacuum servo device and a transfonner having primary and secondary windings and a core magnetically coupling said windings to one another, said oscillator means being connected to said primary winding, said first circuit means being connected to said secondary winding, and said core being connected to said vacuum servo device, whereby said vacuum servo device responds to changes in engine load to move said core within said transformer thereby varying the magnet coupling between said primary and secondary windings to varythe output from said transformer, said output varying the direct current bias in said second circuit means to provide a potential which modulates the pulses from the pulse generator means to provide electronic advance for the ignition system, dependent on both engine vacuum and r.p.m.

4 7. The capacitor discharge ignition system of claim 1 wherein said semiconductor is a first silicon-controlled rectitier having input, output and control electrodes, said control electrode being coupled to said second circuit means. and-said trigger circuit means further includes a second silicon-controlled rectifier having input, output and control electrodes,

said control electrode being connected to the output electrode of said first silicon-controlled rectifier, said input electrode and a potential source connected thereto,'said wiper arm being connected to the ignition capacitor, and said output 

1. A capacitor discharge ignition system for An internal combustion engine having pulse generator means driven in synchronism with the engine for producing electrical pulses, including in combination, trigger circuit means including a semiconductor having a control electrode for operating the same, first circuit means coupling the pulses from the pulse generator means to the control electrode of said semiconductor, said trigger circuit means being responsive to the pulses on the control electrode of said semiconductor reaching a given level to operate the same to discharge the ignition capacitor thereby producing an ignition pulse for the engine, the generated pulses reaching said given level in a timed relation to the engine r.p.m. to provide ignition timing, second circuit means connected to the junction of said first circuit means and the control electrode of said semiconductor for establishing a direct current bias on the control electrode, and vacuum controlled voltage generator means connected to said second circuit means, said vacuum-controlled means being responsive to the engine vacuum under changing engine loads to vary the direct current bias in said second circuit means, hence on the control electrode of said semiconductor thereby varying the time required for the pulses from the pulse generator means to reach the given level to discharge the ignition capacitor so the ignition timing depends on both engine r.p.m. and vacuum.
 2. The capacitor discharge ignition system of claim 1 wherein said vacuum-controlled voltage generator means includes a vacuum servo, a potentiometer having a wiper arm and a potential source connected thereto, said wiper arm being connected to said vacuum servo and being moved by the same to produce a potential proportional to the engine vacuum.
 3. The capacitor discharge ignition system of claim 1 wherein said vacuum-controlled voltage generator means comprises oscillating circuit means including piezoelectric means for establishing the output frequency thereof, integrating circuit means connected to the output of said oscillating circuit means and having a voltage output dependent on the input frequency from said oscillator circuit means, and transducer means responsive to engine vacuum connected to said piezoelectric means so the mechanical motion thereof in response to changes in engine vacuum strains said piezoelectric means to change the frequency of the same thereby varying the output frequency of said oscillating circuit means to vary the output potential of said integrating circuit means in accordance with engine load.
 4. The capacitor discharge ignition system of claim 1 wherein said vacuum-controlled voltage generator means includes amplifier circuit means including a strain sensitive semiconductor having a mechanical input for modulating the bias thereon, transducer means responsive to engine vacuum, and means connecting said transducer means to said mechanical input of said semiconductor, said transducer means responding to changes in the engine load to vary the strain on said semiconductor through said mechanical input thereby changing the bias thereon to regulate the output potential of said amplifier circuit means in accordance with engine vacuum.
 5. The capacitor discharge ignition system of claim 1 wherein said second circuit means includes an electron control device having input, output and control electrodes, with the control electrode of said semiconductor being connected to said output electrode of said electron control device, a potential source coupled to said input electrode, and said vacuum-controlled voltage generator means being connected to said control electrode thereof, said vacuum-controlled means being responsive to engine vacuum to produce a potential to control the conduction of said electron control device thereby varying the bias on the control electrode of said semiconductor.
 6. The capacitor discharge ignition system of claim 1 wherein said vacuum-controlled means includes oscillator means, a vacuum servo device and a transformer haVing primary and secondary windings and a core magnetically coupling said windings to one another, said oscillator means being connected to said primary winding, said first circuit means being connected to said secondary winding, and said core being connected to said vacuum servo device, whereby said vacuum servo device responds to changes in engine load to move said core within said transformer thereby varying the magnet coupling between said primary and secondary windings to vary the output from said transformer, said output varying the direct current bias in said second circuit means to provide a potential which modulates the pulses from the pulse generator means to provide electronic advance for the ignition system, dependent on both engine vacuum and r.p.m.
 7. The capacitor discharge ignition system of claim 1 wherein said semiconductor is a first silicon-controlled rectifier having input, output and control electrodes, said control electrode being coupled to said second circuit means, and said trigger circuit means further includes a second silicon-controlled rectifier having input, output and control electrodes, said control electrode being connected to the output electrode of said first silicon-controlled rectifier, said input electrode being connected to the ignition capacitor, and said output electrode being connected to the high voltage transformer of the ignition system for producing a firing pulse for the engine. 